The mechanisms underlying non-insulin dependent diabetes mellitus (NIDDM) remain controversial and, despite progress in the molecular genetics of NIDDM, the mechanisms are unknown for >85% of patients. This project assesses the relationship of hyperproinsulinemia to insulin secretory function in a population at high risk for progression to NIDDM, namely euglycemic women with previous gestational diabetes (GDM) as a potential marker for localizing beta cell defects to steps which do versus those that do not impact on post-translational processing of the insulin gene product.